(a) Field of the Invention
The present invention relates to LCD manufacturing, and in particular, to a glass substrate test apparatus and method for optically inspecting defects of an alignment layer before charging liquid crystal into a liquid crystal cell.
(b) Description of the Related Art
Typically, LCD manufacturing includes thin film transistor (TFT) array fabrication, color filter fabrication, and liquid crystal cell fabrication processes.
The TFT fabrication process is similar to the process used to fabricate semiconductor devices where various steps are repeatedly performed, such that it is possible to control a yield by making a decision on proceeding to a next process or reworking the same process by capturing defects immediately after each unit process.
That is, since the basic TFT fabrication process includes the steps of depositing metal and organic material layers and patterning the same, it is possible to inspect defects of the patterns immediately after a photolithography step by measuring electric resistance or through visual analysis.
Accordingly, it is possible to achieve an ideal yield in the TFT fabrication process if the production yield of each step is set to be 100%. In other words, the processing achievement can be electrically and optically determined because the processing of TFT fabrication consists of patterning processes.
The color filter fabrication process includes depositing black matrix and color resin and patterning the deposited layer using photolithography methods, so defect inspection can also be performed after each unit process, as in the TFT fabrication process.
An optical surface analysis rather than an electric analysis is used for inspecting unevenness of the surface or areas where the color resin is badly deposited. Accordingly, there is no difficulty to achieve an ideal yield at each unit process.
On the other hand, there can be two kinds of defect inspection methods in the liquid crystal cell process.
Liquid crystal cell processing consists of two processes, i.e., a glass substrate process including the steps of depositing, curing, rubbing an alignment layer, and assembling the liquid crystal cell; and a process after cutting in unit of crystal cell and before modularizing the crystal cell.
In the second process of liquid crystal cell processing, there is no difficulty to achieve an ideal yield by monitoring the defects at each unit process, because most defect inspection is performed using visual surface analysis at every unit process.
In the first process of liquid crystal cell processing, however, the defects caused while depositing, curing, and rubbing the alignment layer can be optically inspected during the processes. That is, defects such as non-uniformity of the alignment layer caused by pre-cure and cure processes and particles generated in the rubbing process or by other causes during the processes can be inspected using visual surface analysis. However, componential anisotropy can exist on the alignment layer, caused by remaining solvent that does not evaporate because of a difference in curing speed even though the surface of the alignment layer appears even. The componential anisotropy of the alignment layer generates electrostatic alignment anisotropy when charging the liquid crystal material so as to locally destroy alignment on the alignment layer, resulting in stains having different luminance distributions from other areas.
In the conventional inspection method, this kind of stain cannot be detected immediately after the alignment layer cure process. If the stain is detected after the liquid crystal is charged, it is impossible to rework the glass substrate so the yield cannot be improved.
In the alignment layer rubbing process, since uniform furrows having a depth of 50˜60 Å are formed, it is impossible to detect defects immediately after the rubbing, but rather an insufficiency of alignment can only be detected by an electrostatic correlation of the rubbing direction and the liquid crystal after the liquid crystal is charged into the liquid crystal cell. Accordingly, in this method, rubbing rework is impossible, and even though the defects are detected, it does not help in improving the yield.
The substantial reason why the defects cannot be detected immediately after each unit process is that the defects of the alignment layer are inspected using optical analysis on the basis of the correlation of the alignment layer and the liquid crystal.